1. Field of Invention
The present invention relates to a one-way torque tool and, more particularly, to a one-way torque tool that requires a small angle of neutral rotation before active rotation can be executed again.
2. Related Prior Art
A conventional torque tool is often used to drive a nut or screw. For example, a wrench may be used to drive a nut or screw. A screwdriver may be used to drive a screw. An Allen key may be used to drive a screw.
A one-way torque tool is often used to drive a nut or screw in a limited space. A one-way torque tool may be a one-way (or “ratchet”) wrench or screwdriver. For example, a one-way wrench includes a handle extending from a hollow head, a rotor rotationally placed in the head, and a one-way driving unit or transmission arranged between the head and the rotor. A one-way screwdriver includes a handle, a rotor rotationally placed in the handle, and a one-way driving unit or transmission arranged between the handle and the rotor. The one-way transmission generally includes a pawl pivotally connected to the head or handle and a toothed wheel co-axially connected to the rotor. In operation, then rotor is engaged with a nut or screw via a socket for example, and the handle is rotated to and fro. The rotor is driven by the handle via the one-way transmission as the pawl is engaged with the toothed wheel when the handle is rotated in an active direction. The rotor is not driven by the handle via the one-way transmission as the pawl is disengaged from the toothed wheel when the handle is rotated in a neutral direction.
As disclosed in U.S. Pat. No. 6,655,238, a ratchet tool includes a head 30, an engaging ring 40, a pawl 50 and a spring 34. The engaging ring 40, the pawl 50 and the spring 34 are placed in the head 30. Biased by the spring 34, teeth of the pawl 50 are engaged with teeth of the engaging ring 40.
As disclosed in U.S. Pat. No. 4,147,076, a reversing-ratchet wrench includes a lever 10 formed with a fulcrum end 12, a pawl carrier 20 placed in the fulcrum end 12, a double pawl element 27 supported on the pawl carrier 20, and a ratchet drive selector mechanism 30 connected to the double pawl element 27. The ratchet drive selector mechanism 30 is used to bring teeth formed on a selected one of two ends of the double pawl element 27 with teeth formed on an internal side of the fulcrum end 12. Thus, the reversing-ratchet wrench is switched between a tightening mode and a loosening mode. A similar wrench can be found in U.S. Pat. No. 4,261,233.
U.S. Pat. No. 5,074,174 discloses a socket wrench including a body 1, a ratchet member 108 and a plurality of socket members 102, 103 and 104. The ratchet member 108 and the socket members 102, 103 and 104 are placed in the body 1. The ratchet member 108 includes two pawls 180 and 181 and a cam 182. By operating the cam 182, teeth of a selected one of the pawls 180 and 181 is engaged with teeth of the socket member 104.
It should be noted that after the handle is rotated in the active direction to drive the nut or screw, the handle must be rotated in the neutral direction for the angle of at least one tooth to return the pawl into engagement with the toothed wheel before the handle can be rotated in the active direction to drive the nut or screw again. For example, if the toothed wheel includes twenty-four teeth, i.e., the angle of each tooth is 15°, the handle must be rotated in the neutral direction for at least 15° before the handle can be rotated in the active direction to drive the nut or screw again. There is however not enough space for the rotation of the handle in the neutral direction for the angle of one tooth.
The number of the teeth can be increased to reduce the angle of a tooth. As disclosed in U.S. Pat. No. 6,666,111 for example, the number of the teeth is 90 to 180 so that the angle of one tooth is 4° to 2°. As the number of teeth is large, the size of the teeth is small, and the strength of the teeth is low. The teeth could easily be worn away.
Furthermore, for each of the conventional torque tools, the number of the teeth is constant, i.e., the angle of one tooth is constant. A user may not be able to exert large torque if he or she chooses to use a toque tool with a large number of teeth such as disclosed in U.S. Pat. No. 6,666,111 in limited space. Hence, there is an unsatisfied need for a torque tool to allow a user to exert large torque in limited space. The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.